<div class="dropzone">
  <div id="draggable" draggable="true" ondragstart="event.dataTransfer.setData('text/plain',null)">
    This div is draggable
  </div>
</div>
<div class="dropzone"></div>
<div class="dropzone"></div>
<div class="dropzone"></div>

<style>
  #draggable {
    width: 200px;
    height: 20px;
    text-align: center;
    background: white;
  }

  .dropzone {
    width: 200px;
    height: 20px;
    background: blueviolet;
    margin-bottom: 10px;
    padding: 10px;
  }
</style>

<script>
  var dragged;

  /* 拖动目标元素时触发drag事件 */
  document.addEventListener("drag", function( event ) {

  }, false);

  document.addEventListener("dragstart", function( event ) {
      // 保存拖动元素的引用(ref.)
      dragged = event.target;
      // 使其半透明
      event.target.style.opacity = .5;
  }, false);

  document.addEventListener("dragend", function( event ) {
      // 重置透明度
      event.target.style.opacity = "";
  }, false);

  /* 放置目标元素时触发事件 */
  document.addEventListener("dragover", function( event ) {
      // 阻止默认动作以启用drop
      event.preventDefault();
  }, false);

  document.addEventListener("dragenter", function( event ) {
      // 当可拖动的元素进入可放置的目标时高亮目标节点
      if ( event.target.className == "dropzone" ) {
          event.target.style.background = "purple";
      }

  }, false);

  document.addEventListener("dragleave", function( event ) {
      // 当拖动元素离开可放置目标节点，重置其背景
      if ( event.target.className == "dropzone" ) {
          event.target.style.background = "";
      }

  }, false);

  document.addEventListener("drop", function( event ) {
      // 阻止默认动作（如打开一些元素的链接）
      event.preventDefault();
      // 将拖动的元素到所选择的放置目标节点中
      if ( event.target.className == "dropzone" ) {
          event.target.style.background = "";
          dragged.parentNode.removeChild( dragged );
          event.target.appendChild( dragged );
      }
    
  }, false);
</script>